Process for producing torque stretch yarns

ABSTRACT

A PROCESS IS DISCLOSED FOR PRODUCING UNIFORM TORQUE STRETCH YARNS USEFUL FOR KNITTING STRETCH-APPAREL, SUCH AS LADIES&#39;&#39; SHEER HOSIERY. YARN IS FALSE-TWISTED WITH A FLUIDTORQUE JET DEVICE AND THE TWIST IS HEAT-SET IN A JET OF   HEATED FLUID. CONTINUOUS HIGH SPEED OPERATION OF THE PROCESS, IN COMBINATION WITH A DRAWING OPERATION, IS ILLUSTRATED FOR PROVIDING HIGH LEVELS OF SET-TWIST IN LOW DENIER YARN.   D R A W I N G

Sept. 28, 1971 A. H. DUGAS 3,608,299

PROCESS FOR PRODUCING TORQUE STRETCH YARNS Filed April 15, 1970 2 Sheets-Sheet 1 INVENTOR ALFRED H. DUGAS ATTORNEY Sept. 28, 1971 DUGAS 3,608,299

PROCESS FOR PRODUCING TORQUE STRETCH YARNS Filed April 15, 1970 2 Sheets-Sheet 2 FIG-Z BY fihaiM ATTORNEY INVENTOR ALFRED H. DUGAS 3,668,299 Patented Sept. 28., 1971 3,608,299 PROCESS FOR PRODUCING TORQUE STRETCH YARNS Alfred H. Dugas, Martinsville, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. Filed Apr. 15, 1970, Ser. No. 28,583 Int. Cl. D02g 3/02 US. Cl. 57-157F 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention rel-ates to a process for producing torquestretch yarns, and more particularly to improvement 1n twist-setting operations used in the manufacture of twist lively yarns for stretch apparel such as ladies sheer hosiery.

Production of torque-stretch yarns involve (1) inserting twist into a yarn of thermoplastic filaments, (2) heat setting a twisted configuration in the filaments, (3) cooling the twisted yarn below the second-order transition temperature of the thermoplastic material, and (4) untwisting the yarn to impart twist-liveliness. The degree of stretch in hosiery or other stretch-fabric produced from the yarn is related to the amount of twist, or torque, permanently set into the yarn. For yarn used in sheer stretch hosiery, it has long been desirable tohave a high level of uniform set twist which has required the use of expensive equipment operated at relatively low speeds.

Breen and Sussman US. Pat. No. 3,279,164 discloses a process in which yarn passes continuously over a hot plate and then through a fluid torque jet which introduces false twist so that the yarn is twisted during passage over the hot plate. The yarn is heat-plasticized to set the twist as it passes over the hot plate, is cooled to deplasticize the yarn by supplying cool fluid to the torque jet device, and is then untwisted as it passes away from the jet device. This process has important advantages over ones using mechanical twisting devices in that a torque jet can introduce and remove twist at tremendous speeds while simultaneously cooling the yarn, the jet device is quite small, and there are no moving mechanical parts to chafe the yarn or limit processing speeds. However, the speed of yarn travel is limited by the rate at which the yarn can be heated uniformly to the temperature required for heatsetting the twist. This temperature must be maintained within narrow limits for the production of high quality stretch yarn. The elficiency of converting applied twist to set twist decreases rapidly as the temperature is lowered. On the other hand, too high a temperature will cause hard spots in the yarn or erratic operation due to filaments sticking together. Long hot plates have been found necessary to provide the required uniformity when operating at economical yarn speeds.

The operation of the torque jet is extremely sensitive to the tension on the yarn and the position of the yarn in the jet device. The tension must be maintained uniform and the yarn must be kept precisely centered along the jet axis in order to obtain a uniform stretch yarn. The intensity of twist imparted by the jet varies inverses with the yarn tension, and high set twists require the lowest possible tensions. The hot yarn must not contact the heating surface or a guide during passage over the hot plate and through the torque jet, since such contact would damage the yarn or cause fluctuations in twist, resulting in a non-uniform yarn. Breen and Sussman disclose yarn guiding means before the hot plate and after the jet device, with the yarn traveling a long free path between the guides. The patent teaches that the yarn tension should be below 15 grams but that tensions below about 3 grams result in non-steady state conditions or twist-doubling. This lower limit seriously restricts the set twist obtainable.

The present invention provides improvements for maintaining highly uniform operation at much lower yarn tensions, so that surprisingly high set twists are obtained in premium quality stretch yarn, even at unusually high yarn processing speeds.

SUMMARY OF THE INVENTION The present invention is a process for producing torquestretch yarn from drawn yarn of thermoplastic synthetic polymer, wherein yarn supplied by feeding means at uniform speed is twisted and heat-plasticized to set twist in the yarn, cooled to deplasticize the yarn, and the twist is removed, in a continuous operation by the combined action of a pair of jet devices. A first jet device provides a symmetrical jet of hot fluid for plasticizing the yarn. This jet is aligned so that the yarn path is along the axis of the plasticizing stream. The yarn is conducted along a straight path from the feeding means through the plasticizing stream and then directly to a torque jet device aligned so that the fluid vortex axis coincides with the axis of the plasticizing stream. The yarn passing through the plasticizing stream of the first jet device is highly twisted by the twisting action of the torque jet, and this twist is automatically removed as the yarn passes beyond the torque jet. The torque jet is supplied with cool fluid to deplasticize the yarn. The combined action of the jets is best when they are close together and the torque jet is shielded from the jet of hot fluid by a plate between the jets which has an opening for passage of the yarn. The deplasticized yarn is withdrawn at a uniform speed which maintains a substantially uniform low tension between the jets and so that the yarn follows a straight path through the jets.

The process is suitable for producing torque-stretch yarn composed of heat-settable material, such as any of the conventional textile yarns of thermoplastic synthetic polymer. A drawn feed yarn is used; preferably the yarn is drawn at least 2X just before the start of the process, as by coupling the process to a drawing process. The combined processes are preferably operated at yarn speeds of 200 to 1000 yards per minute, although lower and much higher speeds can be used. As illustrated in the ex- .amples, the process of this invention is particularly useful in the manufacture of twist-lively yarns for ladies stretch hosiery, wherein the feed yarn used is multifilament or monofilament nylon yarn of less than 35 denier, although yarns of higher denier can be processed acceptably.

The production of torque-stretch yarn for high quality sheer stockings requires extremely uniform processing conditions. The yarn passing through the torque jet must be maintained centered along the vortex axis under uniform tension, since the twist imparted is quite sensitive to variations in either condition. Precise alignment of the yarn with the axes of the two jets is necessary; the annular symmetrical orifice in the heating jet and the vortex in the torque jet then keep the yarn centered, even at extremely low tensions. Consequently, by proper alignment and design of the two jets, contact of the yarn with the walls of the jets is prevented and very uniform yarn is obtained. Contact of hot yarn with solid surfaces would cause stick-slip fluctuations in tension and otherwise impair yarn uniformity. If the yarn cranks to such an extent in the torque jet that the yarn intermittently touches the 3 walls, the direction of twisting is reversed and a very non-uniform set twist results.

The combination of jet treatments of the present invention overcomes the previous difficulties so that high quality torque-stretch yarn can be produced at torque jiet tensions low enough to provide high set twists. The jet heater is surprisingly eflicient in heating the yarn uniformly to plasticizing temperature. Air supplied to the device at to 100 pounds per square inch gage pressure is jetted at approximately sonic velocity, which provides excellent heat transfer. At fluid temperatures of 150 to 250 C., measured at the exit of the jet, the yarn is almost instantaneously plasticized by heating above the secondorder transition temperature, e.g.,, during a yarn travel of only 3 inches (7.6 cm.), if desired. The distance between the two jet devices can be made quite short, e.g., 1 to 6 inches (2.5 to cm.). Hence the jet treatment can be made quite compact and the relatively short free path of the yarn makes lower tensions possible. The high velocity symmetrical jet stream from a properly designed jet device will keep the yarn centered along the stream axis and will prevent yarn contact with the walls of the jet. This further reduces the minimum operable tensions which can be used in the process. A substantially uniform tension between the jet devices of 0.3 to 1.5 grams total tension, and not less than 0.015 gram per denier, is suitable for imparting high uniform set twists to yarn. Preferably the yarn tension is less than 1.0 gram. As illustrated in the examples, this is provided by withdrawing the deplasticized yarn at a speed which is from 2% to 24% less than the speed of the yarn at the feeding means, the particular value depending upon the yarn being processed and its velocity through the treatment zone.

The high velocity plasticizing stream must be symmetrical and aligned so that the yarn is forwarded along the axis of the stream. This is accomplished with a jet device having a chamber for hot fluid, a tubular passage leading from the chamber for jetting a symmetrical stream of hot fluid, and a hollow yarn-guiding member for centering the yarn in the exiting stream. The tip of the yarn-guiding member is centered in the mouth of the tubular passage with a uniform annular space between the two for hot fluid to exit into the passage. The axis of the passage is aligned with the axis of the torque jet so that the yarn is forwarded in a straight line to the torque jet.

Jet devices have been used previously for heat-plasticizing yarn in nonanalogous processes. Breen and Lauterbach -U.S. Pat. No. 3,491,194 discloses a variety of jet devices for heating yarn with a hot turbulent stream in which the yarn filaments are separated and Whipped about by the turbulent fluid. The purpose is to improve the dyeability of the yarn. The jet device shown in FIG. 2 is similar in some respects to a jet device disclosed for use in the process of the present invention. As shown in FIG. 2, however, the tip of the yarn guiding member is olfcenter with respect to the axis of the exit passage, which produces an eccentric flow pattern of the hot fluid into the exit orifice, and the turbulent action of the stream is accentuated by the diverging shape of the exit passage. The yarn is pulled to one side after it exits from the jet device, so the yarn is not forwarded along the axis of the stream. In view of the teaching of the prior art, it is surprising that a jet device can be used for heat-plasticizing yarn in a process in which the filaments are not separated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a preferred apparatus for practicing the process of the present invention.

FIG. 2 is a sectional view of a fluid-torque jet device for false twisting yarn, the cross-section being taken through the axis of the yarn passageway.

FIG. 3 is a sectional view of a fluid jet device for heatplasticizing and forwarding the yarn, the cross-section being taken through the arses er the passages.

4 DETAILED DESCRIPTION FIG. 1 illustrates a preferred embodiment wherein the process of this invention is coupled to a conventional drawing operation. Yarn 10 of thermoplastic synthetic polymer is supplied from any convenient source, such as a package of as-spun yarn, or the yarn may be supplied from the melt-spinning or other process used for making it, without intermediate packaging. The treatment zone where twist is applied and heat-set is after drawing as the yarn travels from draw-roll 11 to yarn-reversing guide 15. The yarn is false-twisted by torque jet 16, shown in more detail in FIG. 2, and is heat-set by heater 17, a jet device shown in FIG. 3.

As shown in FIG. 1, the yarn to be drawn passes from guide :18 through the nip between driven feed-roll 21 and cott-roll 20, around draw pin 14, where drawing is localized, and then makes a series of wraps around driven draw-roll 11 and its associated separator-roll 23. The draw ratio is the ratio of the peripheral velocity of the draw-roll to that of the feed-roll 21.

In the treatment zone, twist inserted in yarn 10 by fluidtorque jet 16 accumulates upstream of jet 16 so that yarn passing through heater .17 is pretwisted. A twist-stop means is required at the entrance of the treatment zone in order to prevent transmission of twist back around draw-roll {11. Any of a number of well-known twist-stop devices may be used. A particularly simple and effective device is a resiliently surfaced twist-stop roll 13 which is urged against the surface of draw roll 11 by a springdevice '(not shown). For threadline stability, the nip between these two rolls 11 and 13 should be substantially at the point of tangency between draw-roll 11 and the straight path of travel of yarn 10 through the treatment zone.

In the heater 17, twisted yarn 10 is very quickly heated to an eifective yarn temperature exceeding the secondorder transition temperature whereby yarn 10 becomes heat-set in its twisted configuration. Passage through fluidtor-que jet 16 inserts the twist and, because the fluid is unheated, quickly cools yarn 10 to stabilize the twisted heatset configuration. Passing downstream from jet 1'6, yarn 10 immediately untwists by the same number of turns inserted upstream, as is well understood in the falsetwisting art. Any real twist present in the yarn supply is, of course, transmitted with the yarn to, through and beyond the treatment zone. The treatment zone terminates with a yarn-reversing guide 15 over which yarn 10 is withdrawn at a yarn speed which equals the peripheral velocity of relaxing-roll 12. Snubbing pins 26 can be used between guide 15 and roll 12 for precise control of tension, as is well understood. For positive control of the withdrawal yarn speed, yarn 10 takes several Wraps around relaxing-roll 12 and its associated separator-roll 22. Draw-roll 11 and relaxing-roll 12 may be separately driven through a suitable geared drive. In the preferred process shown, the two rolls are coaxial and stepped so that they rotate at identical angular velocities and maintain a fixed ratio of first and second yarn speeds by differences in diameter only. Exiting through suitable guide 27, yarn 10 may be wound into a package 28 or may be forwarded for further processing.

Hot fluid is ejected from the exit of heater 17 toward fluid-torque jet 16; and some unheated fluid passes from fluid-torque jet 1 6 back toward heater 17. The length of yarn path between these two devices is preferably short, e.g., from 1 to 6 inches (2.5 to 15 cm.). To prevent adverse effects of these hot and cold fluids upon the opposite devices, a yarn-cleaner 19 may be interposed there- -between. A yarn-cleaner is simply a plate of relatively large area which has a central opening large enough for yarn to pass without contacting it but small enough to remove any fluif or other debris carried on the surface of the yarn.

In FIG. 1, the stationary frame on which the parts are mounted is omitted for clarity, except for upper rail 29. Likewise, drive means for rotating parts are omitted. Suitable mounting and drive means are familiar to those skilled in the art, and a wide variety of designs may be employed.

A typical, relatively uncomplicated, and preferred fluidtorque jet 16 for use in the process of this invention is shown in FIG. 2 in enlarged cross-section at a central plane, view along the direction of yarn travel. Dimensions A and B of a typical assembly are about 0.9 and 0.5 inch (2.3 and 1.3 crm), respectively. A typical thickness is about 0.25 inch (0.6 cm.) exclusive of mounting devices (not shown). Even these relatively minute dimensions are much greater than required for operation, but are deliberately oversized to facilitate handling and to prevent loss by accidental dropping, etc. A generally rectangular body 50 is provided with fitted pipe-means 51 for injection of a pressurized unheated or cooled fluid. Preferred fluids are gaseous, more preferably air. A smaller bore 53 continues from bore 52 and is closed at its other end by plug 54. Cylindrical hole 60 extends through the device as the yarn passage and has an open side communicating with bore 53. Hole 60 and bore '53 are of about equal diameters with the opening along the side of hole 60 being about tangent to the axis of bore 53. Preferably hole 60 is formed in unitary, closely-fitting disc 59 to which handle 58 is attached. Movement of handle 58 to stop 55 rotates the open side of hole 60 into alignment with slot 56 for easy string-up with yarn. Opposite rotation to stop 57 brings hole '60, with yarn passing therethrough, to its operative position as shown. Air forced through bores 52 and -3 under pressure enters the hole 60 approximately tangentially to create a highvelocity swirl in direct contact with the yarn.

'While the torque jet of FIG. 2 is of a preferred construction, the process of this invention is not dependent on use of this patricular design of torque jet. Likewise suitable, for instance, are torque jets described by Nagahara et al. in US. Pat. No. 3,206,922, wherein the entrance opening for yarn travel is constricted relative to a wide-open exit. Breen et al. US. Pat. No. 3,279,164 also describes suitable alternative forms of torque jets.

FIG. 3 is a vertical cross-section of a preferred device for the heating zone of this invention. Yarn enters tubular and, preferably, slightly conical passage 69; and exits via tubular passage 61, which is preferably of uniform diameter. The tubular members providing aligned passages 69 and 61 are conically tapered in mating fashion at their adjacent ends to define a uniform annular opening 62 converging conically along the direction of yarn travel and communicating both with passages 69 and 61 and with enclosed plenum 63. Solid fixed body 64 is provided with an internal duct 65 which passes around an electrical-resistance heater 66 and opens at one end into plenum 63. Opening 67 denotes a duct leading to an external fitting through which pressurized fluid, e.g., air, is forced into duct 65. The fluid is uniformly and rapidly heated while passing over heater 66 and within heated body 64. The hot fluid enters plenum 63, goes through annular opening 62, and flows concurrently with, in contact with all surfaces of, and at a relatively high speed with respect to the forwarded yarn 10. Thermal insulation 68 is preferably applied over all exposed surfaces. A' thermocouple or similar temperaturesensitive device (not shown) is incorporated within plenum 63 and serves, by conventional regulation (not shown), to adjust current flow to heater 66 such that fluid entering annular opening 62 is maintained at a constant predetermined temperature. By way of indicating the small size of this jet device, one preferred heater has dimension C of about 3 inches (7.6 cm.).

The jet devices through which yarn passes in the treatment zone of this invention have very small openings. It is very critical to the effective operation of this process that all yarn passages in the treatment zone be extremely carefully aligned axially to provide straight travel of the yarn with substantially no contact with solid surfaces. Contact of yarn with jet device 17 at the entrance opening 69 (FIG. 3) is not detrimental to yarn quality, and a yarn guide may be used at this point, but further contacts throughout the remainder of the treatment zone must be carefully avoided in order to obtain highly uniform yarn.

As used herein, the term yarn refers to an assembly of substantial length and small cross-section of filaments with or without some real twist. Preferred yarns are of continuous filaments, i.e., either monofilament or multifilament yarns. Especially in the case of multifilament yarns, a low level of real twist is often present in the supply yarn to facilitate handling.

Yarns suitable for processing according to this invention must be heat settable; i.e., capable of the neutralization of torque stresses by exposure to elevated temperatures. Because this process is particularly suited to false-twisting of yarns for ladies sheer hosiery, and because most of such yarns are currently of polyamides, preferred yarns are of polyamides, i.e., polymers of at least film-forming molecular weight characterized by a linear molecular structure linked by recurring amido groups. The most widely known (and suitable) polyamides are polyhexamethylene diamine (66-nylon) and polycaprolactam (6-nylon). Another preferred polyamide is a random copolymer of 6-nylon with 66-nylon in which the 6-nylon polymer units are present at 5 to 15% by weight of the copolymer. This copolymer responds very well to false-twisting processes, whereby it can be processed at lower temperature. It also has the advantages over homopolymeric yarns, in fabrics knit therefrom, of high residual shrinkage (useful in customary hose-boarding, for example) and a soft hand (i.e., a softer tactile sensation). Many other polyamide homopolymers and copolymers are likewise suitable as, also, are other polymers such as polyesters (e.g., polyethylene terephthalate), polyacrylics (e.g., polyacrylonitrile), and the like.

The present process maximizes the efiiciency of twist setting by operating at the unprecedentedly low tensions of 0.3 to 1.5 gm. in the treatment zone. Preferably the tension is less than 1.0 gm. Processes in which the yarn experiences substantial contact with solid surfaces (e.g., hot plates or well-known false-twist spindles) inherently require much higher yarn tension. Peripheral velocity (V of draw-roll 11 and that (V of relaxing-roll 12 are directly controlled, V always being sufficiently less than V to produce a tension in the treatment zone within the required range. Percent relaxation (R), as used herein, is defined according to The substantial elimination of contacts bythe yarn with solid surfaces in the treatment zone also provides two further advantages. First, the uniformity of twist along the yarn is significantly improved by eliminating stick-slip behavior. Secondly, the performance of this process is unaffected by yarn friction. In known false-twisting processes, the proper selection of yarn finish to control friction and fuming is very critical.

In the examples, relative viscosity (RV) is defined as the ratio of absolute viscosities at 25 C. of polymer solution and the solvent employed. For nylon, the solvent is formic acid (containing 10% by weight water) and the solution contains 8.4% by weight nylon.

Set-twist is measured as follows: A sample (eg. 24- inches or 6l-cm. long) is removed from its package and held at its mid-point to prevent twisting while both ends are taped together and to a support. A 0.-6-mg./denier (this denier is twice the yarns denier) weight is hung from the mid-point. In short increments working up from the weight, the yarn is allowed to relax and twist, any

snarls being gently Worked out before progressing to the next increment. Finally, the completely relaxed yarn is exposed to a gentle flow of atmospheric steam until no further twisting occurs. Set-twist in turns per unit length of fully extended yarn is measured using a commercial twist-counter set at a yarn tension of 6 gm. Set-twist measured by this test provides a good correlation with finished hose characteristics.

EXAMPLE I Using a process as described in connection with the drawing, the heater 17 and fluid-torque jet 16 being mounted on a standard draw-twister, a 3-filament nylon yarn is false-twisted. The nylon used is a random copolymer composed of 90% by weight 66-nylon polymer units and 10% by weight 6-nylon polymer units. Its relative viscosity, RV, is 39.5. It contains, based on the weight of the polymer, 0.3% titanium dioxide, 0.10% sodium phenylphosphinate, and 0.003% manganese hypophosphite.

In the drawing zone, the yarn is drawn 4.474X to 18.2 denier, the peripheral velocity of the draw-roll 11 being 248 yd./min. (227 m./min.). Heater 17 provides constant air temperature in plenum 63 such that the moving yarn attains a temperature of 141 C. measured 3 inches (7.5 cm.) beyond the heater. Air pressure of the supply to heater 17 is adjusted to provide air velocity from slot-opening 62 which is less than but about sonic velocity. Air pressure of unheated air injected into fluid-torque jet 16 is 90 p.s.i.g. (6.3 kg./cm. gauge), the yarn passage 60 being about 0.025 inch (0.064 cm.) in diameter and 0.25 inch (0.64 cm.) long. A perforated disc yarncleaner 19 with about 0.01 inch (0.025 cm.) opening is positioned about midway between heater 17 and fluid torque jet 16. The heater, torque jet, and yarn-cleaner are exceedingly carefully aligned so that the straight line of yarn travel, tangent to draw-roll 11 at the point of departure and extending to yarn reversing-guide 15, passes along the axis of each yarn passage with a lateral offset less than plus or minus 0.005 inch (0.013 cm.). The coaxial draw and relaxing rolls diifer in diameter to yield 20% relaxation of the yarn in the treatment zone, the yarn tension measured about 1 inch (2.5 cm.) prior to entering the fluid-torque jet being about 0.9 gram. Under these conditions, a set-twist of 71 turns/inch (2795 turns/ meter) is developed.

Physical properties of the processed yarn are obtained from stress-strain curves recorded by an Instron Tensile Tester at a constant rate of elongation of 60% per minute. Yarn on its package is conditioned one day at 75 F. (23.9 C.) and 72% relative humidity, and the tests are run in the same atmosphere.

Yarn denier 20.0 Breaking strength gm.) 107 Tenacity (gm./den.) 5.4 Elongation (percent) 41 Initial modulus (gin/den.) 9.2

Both elongation and initial modulus are measured from the point where twist-crimp is removed and stress-strain response of the straightened yarn commences.

Ladies sheer hosiery are knit from the yarn of this example with plain stitch on a two-feed knitting machine, the stitch courses being alternately of S- and Z-twist yarns. The resulting finished stretch hose are rated fully equivalent to premium commercial sheer hose knit from 203 nylon stretch yarns. Strain-recovery and stress-decay for the hose are determined with an Instron Tensile Tester. A planar leg form (equivalent to National Bureau of Standards form), with two 4-inch (10.16-cm.) diameter holes in the knee area is used for mounting the test hose which is fastened over the form under sufficient longitudinal tension to remove any wrinkles. On one side, tape is affixed around the holes and then hosiery material is carefully cut out from the holes on that one side.

The form is mounted to the crossbar of the tested with a hole centered over a 3.75-inch (9.52-cm.) diameter polished steel hemisphere fastened to a compression cell. With chart speed set at 10 in./min. (25.4 cm./min.) and cross-head speed at 2 in./min. (5.08 cm./min.), the hemisphere is forced into the fabric-covered hole for 0.75 minute, stopped at that point for 1 minute, and then returned to its starting position. Four dimensions in chart-units are measured from the stress-strain chart: (1) strain-units (A) from initial zero stress to the point of maximum stress; (2) stress-units (S at the maximum; (3) stress-units (S at the end of the one-minute hold; and (4) strain-units (B) from stress (S back to zero stress. Percent strain-recovery is computed as 100 (B/A); and percent stress-decay is 100 (S -S )/S For the hose of this example, strain-recovery is 92% and stress-decay 28%. For comparison, the present premium commercial stretch hose exhibits strain-recoveries from 77 to 91% and stress-decays of 28 to 35%.

EXAMPLES II-VI Draw-ro1lspeed405 yd./min. (370 m./rnin.)

Draw-ratio--4.11X

Heater:

Air flow rate0.69 s.c.f.m. (0.020 std. rn. /min.) Supply air pressure-35 p.s.i.g. (2.5 kg./cm. Exit air temperature218 C.

Torque jet:

Air flow rate0.30 s.c.f.m. (0.008 std. m. /min.) Supply air pressure p.s.i.g. (6.3 kg./cm.

Percent relaxation (R) and tension (T) are related to set-twist as follows:

Example R (percent) T (gm.) Set-twist II 16 0.80 54 turns/in. (2,125 turns 'mJ. III 18 0. 55 61 turns/in. (2,400 turns/111.).

A previously drawn 21-denier/3 filament yarn of the same composition as for Examples 11 and III is processed as shown in FIG. 1 except that it is led directly from supply bobbin 18 to draw-roll 11 while by-passing feedroll 21 and draw pin 14. Conditions employed are:

Draw-roll speed-698 yd./ min. (640 m./ min.)

Draw-ratiol .OX

Heater:

Air-flow rate-0.60 s.c.f.m. (0.017 std. m. /min.) Supply air pressure35 p.s.i.g. (2.5 kg./cm. Exit air temperature-Q28 C.

Torque jet:

Air flow rate0.30 s.c.f.m. (0.008 std. m. /min.) Supply air pressure90 p.s.i.g. (6.3 kg./cm.

Resultant set-twist is:

Example R (percent) T (gm.) Set-twist IV 4 1.30 19.5 turns/in. (770 turns/m.). V 6 0.95 27.0 turns/in. (1,065 turns/m.). VI 9 0. 40 38.5 turns/in. (1,515 turns/m.).

Within the operable range of tensions in the treatment zone lower tensions are seen to yield higher levels of set-twist.

EXAMPLE VII A ZO-denier torque-stretch monofilament is prepared as described in Example I, the monofilament being composed of the same 66/6 nylon copolymer. Conditions employed are:

Draw-roll speed-405 yd./min. (370 m./min.) Draw-ratio4.788X Heater:

Air-flow rate-0.69 s.c.f.m. (0.020 std. mF/min.) Supply air pressure-35 p.s.i.g. (2.5 kg./cm. Exit air temperature-216 C. Torque jet:

Air flow rate0.50 s.c.f.m. (0.014 std. m. /rnin.) Supply air pressure90 p.s.i.g. (6.3 kg./cm. Relaxation-20% Tension in treatment zone0.5 gm.

The processed ZO-denier monofilament has a set-twist of 46 turns/inch (1810 turns/meter).

EXAMPLES VIII-IX These examples show the effect of heat-setting temperatures on set-twist and tenacity. Yarn, process, and processing conditions are as described for Example II except as follows:

Heater exit air tempera- Tenacity Example ture, C. (gm./den.) Set-twlst VIII 198 5. 8 44 turns/in. (1,730 turns/m.)- IX 222 5. 4 54 turns/in. (2,125 turns/111.).

Higher temperatures of heat-setting within the operable range are seen to increase the set-twist with some sacrifice in tenacity.

EXAMPLE X The 66-nylon homopolymer yarn of Example II is processed as described there, and as shown in FIG. 1, under the following conditions:

The resulting 21-denier torque-stretch yarn has a set twist of 59 turns/inch (2320 turns/meter).

EXAMPLE XI A 3-filament yarn of poly(methylene-di-1,4-cyclohexylene dodecanediamide) is prepared by melt-extrusion as described by Speck in U.S. Pat. No. 3,393,210. The polymer flake contains 1% by weight of finely-divided kaolinite. The melt is extruded through a spinneret-block maintained at 335 C., and the exit-face of the block is blanketed with steam at 250 C. The extruded yarn is drawn 1.46X in a first stage, annealed at constant length in a hot chest at 160 C. in a second stage, and wound into a package of -denier yarn at 3500 yd./min. (3200 m./min.). The packaged yarn is characterized by a relative viscosity of 80 (determined as described by Knospe in U.S. Pat. No. 3,416,302, column 5, lines 30-37). The packaged yarn is false-twisted as described in Examples 10 IV, V, and VI, i.e., without further drawing. Specific conditions employed are:

Draw-rol1405 yd./min. (370 m./min.)

Draw ratio-1X Heater:

Air flow rate0.70 s.c.f.m. (0.020 std. m. /min.) Supply air pressure35 p.s.i.g. (2.5 kg./cm. Exit air temperature-222 C.

Torque jet:

Air flow rate-0.3O s.c.f.m. (0.008 std. m. /min.) Supply air pressurep.s.i.g. (6.3 kg./cm.

Relaxation-l l Tension in treatment zone0.4 gm.

The resultant 15-denier/3-filament torque-stretch yarn has a set-twist of 47 turns/inch (1850 turns/meter).

EXAMPLE XII A 3-filament yarn of poly( tetramethylene terephthalate) is prepared by melt-extrusion of polymer flake. The undrawn yarn as packaged has an inherent viscosity (m of 1.0 where and 1 is the viscosity of the polymer solution at 25 C.,

no is the viscosity of the solvent at 25 C., and

c is the solution concentration of 0.32 gm. of polymer per ml. of solution.

The solvent is a 75/25 parts per volume (25 C.) mixture of methylene chloride and trifiuoracetic acid, respectively. The packaged yarn is false-twisted according to the procedure of Example I under the folowing specific conditions:

Draw-roll speed248 yd./min. (227 m./min.)

Draw ratio-21286X Heater:

Air flow rate-0.60 s.c.f.m. (0.017 std. m. /min.) Supply air pressure-35 p.s.i.g. (2.5 kg./cm. Exit air temperature198 C.

Torque jet:

Air flow rate0.30 s.c.f.m. (0.008 std. m. /min.) Supply air pressure90 p.s.i.g. (6.3 kg./cm.

Relaxation16% Tension in treatment zone0.65 gm.

The resultant 15-denier/ 3-filament torque-stretch yarn has a set-twist of 68 turns/inch (2675 turns/ meter).

EXAMPLE XIII Monofilament yarn having torque and crimp is processed as follows: Two bobbins of undrawn monofilament feed yarn of the same polymer composition as Example II are plied prior to passing between the feed and cott rolls. The plied ends are drawn and false-twisted under the conditions shown below, then the ends are separated after passing the reversal guide and wound on separate pirns. Final yarn denier of each end is 15.

Draw roll speed-412 y.p.m. (375 m./min.)

Draw ratio'4.347X

Heater:

Air flow rate0.76 s.c.f.m. (0.022 std. m. /min.) Supply air pressure-13 p.s.i.g. (0.94 kg./cm. Exit air teniperature174 C.

Torque jet:

Air orifice diameter-0.015 inch (0.038 cm.) Supply air pressurel00 p.s.i.g. (7.1 kg. cm?) Relaxationl6% Tension in treatment zone-0.95 gram Each end of the resulting yarn has a set twist of 42 turns/ inch (1650 turns/meter). The crimp developed in each end when the yarn is treated as for measurement of set twist is characterized as having 48 crimps/inch (1890 crimps/meter) and crimp diameter of 3.0 mils.

I claim:

1. In the process for producing torque-stretch yarn wherein drawn yarn of thermoplastic synthetic polymer is supplied by feeding means at uniform speed, twisted and heat-plasticized to set twist in the yarn, cooled to dep1asticize the yarn, and the twist is removed in a continuous operation; the improvement which comprises conducting the yarn from the feeding means along treatment path through a symmetrical jet stream of hot fluid to platsicize the yarn, jetting said stream to have an axis aligned so that the yarn path is along the axis of the plasticizing stream, false-twisting and deplasticizing the yarn with a torque jet of cool air, jetting said air to have a vortex axis aligned so that the vortex axis coincides with said axis of the plaitscizing stream, and with drawing the deplasticized yarn at a uniform speed while maintaining the yarn under a substantially uniform tension between the plasticizing stream said torque jets within the range of 0.3 to 1.5 grams total tension and at least 0.015 gram per denier, the combined action of the plasticizing stream and said torque jets being such that a high uniform set twist is imparted to the false-twisted yarn.

2. A process as defined in claim 1 including combining the action of the jets such that there is a distance of 1 to 6 inches between the plasticizing stream and the torque jet and shielding the torque jet from the jet of hot fluid.

3. A process as defined in claim 1 including drawing the said yarn at least 2X just before the start of the process.

4. A process as defined in claim 1 including processing the yarn at 200 to 1000 yards per minute.

5. A process as defined in claim 1 wherein the feed yarn is a multifilament nylon yarn of less than denier.

6. A process as defined in claim 5 including jetting air at a pressure of 5 to pounds per square inch gauge and a temperature of to 250 C. as measured at the exit of the jet to form said plasticizing stream.

7. A process as defined in claim 5 wherein said speed of withdrawing the deplasticized yarn is from 2% to 24% less than the speed of the yarn at said feeding means.

8. A process as defined in claim 5 wherein said tension between the jets is less than 1.0 gram.

References Cited UNITED STATES PATENTS 3,006,137 10/1961 Long 5734X 3,079,746 3/1963 Field, Jr 5734X 3,156,028 11/1964 Weiss et a]. 57-34 3,340,684 9/1967 Shichman 57-34 3,380,242 4/1968 Richmond et al 57l57X STANLEY N. GILREATH, Primary Examiner W. H. SCHROEDER, Assistant Examiner U.S. Cl. X.R. 

